Method of determining an object&#39;s position and associated apparatus

ABSTRACT

A method of determining an object&#39;s position and associated apparatus provides positional information in a form that may be conveniently communicated to a computer to calculate the object&#39;s position. In a preferred embodiment, representatively incorporated in a computer keyboard, a method of determining an object&#39;s position includes forming an optical grid of reflected beacons and detecting an obstruction of the reflected beacons. The preferred embodiment apparatus utilizes a single light source to detect an object&#39;s position in two dimensions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.08/486,310, filed on Jun. 7, 1995, now U.S. Pat. No. 5,734,375.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods of determining anobject's position and, in a preferred embodiment thereof, moreparticularly provides a method and apparatus for optically digitizing anobject's position on a plane above a computer keyboard.

2. Description of Related Art

Pointing devices are well known in the computer art. Their purpose,generally, is to permit the computer user to input positionalinformation to the computer. A pointing device performs this function by"digitizing" an object's relative position in space, that is, by puttingthe positional information in a form that is readable by the computer.

The number of uses for pointing devices have increased as moderncomputer user interfaces have become increasingly graphical. Forexample, a computer user may now use a "mouse" to select a file to openfor editing purposes (by "clicking" on an icon representing the file),instead of typing a file name on a keyboard.

Typical pointing devices currently available to computer users includemouse, trackball, digitizing pad, joystick, touch screen, and eyetracking devices. There are variations of each of these and there arepointing devices that have a combination of features found on more thanone of these. Each, however, has its disadvantages.

A mouse typically has a housing for grasping in the user's hand, and aball underneath the housing for rolling the housing about on a desktop.Rollers inside the housing digitize the mouse's position by translatingthe ball's movement into electrical signals which are then communicatedto the computer. Switches, typically mounted to the housing's topsurface, allow the user to "click" (activate a switch to select an icon,for example) on an object displayed on the computer's screen, or performother functions. The mouse, however, requires the user to devote asignificant portion of a desktop as an area in which the mouse can berolled around. The mouse also requires the user to remove one hand fromthe keyboard while the mouse is being rolled around on the desktopand/or while a mouse switch is being activated, thus slowing down thedata entry process. Furthermore, the mouse requires a means ofcommunicating the electrical signals to the computer, such as a cablewhich must be attached between the computer and the mouse and mustfollow the mouse around the desktop.

A trackball eliminates some of the mouse's disadvantages, butsubstitutes others in their place. The trackball is, essentially, anupside-down mouse, having a stationary housing with the ball facingupward so that the ball can be rolled by the user's fingers. Theswitches are normally placed on the top surface of the housing adjacentthe ball. The rollers which translate the ball's motion into electricalsignals are located in the housing where, due to the large upward-facingopening in the housing through which the ball protrudes, they areexposed to dust and dirt. Some keyboard manufacturers have eliminatedthe need for a separate trackball device cable for communicating theelectrical signals to the computer by building the trackball devicedirectly into the keyboard housing so that a single cable communicatesboth keyboard and trackball input to the computer. The user does,however, still have to move his or her hand away from the keyboard inorder to roll the ball. Another disadvantage is that a large amount ofdexterity is required to manipulate the trackball while clicking on ascreen object, if only one hand is used.

A digitizing pad typically utilizes a rectangular planar area on thesurface of a hard plastic housing, which, in turn, is placed on theuser's desktop. The pad uses one of several methods to sense theposition of a pen or stylus on the pad surface. In some pads, thepressure of the pen or stylus on the pad surface makes contact orchanges capacitance in many fine, closely spaced conductors beneath thepad's surface. In some others, the pen or stylus carries a magnetic orelectromagnetic field source which is sensed by the pad, thus, the penor stylus position is sensed due to the proximity of the pen or stylusto the pad. Among the digitizing pad's disadvantages is the space on thedesktop taken up by the pad's housing. Additionally, the user mustremove his or her hand from the keyboard to operate the pen or stylus.

A joystick is another pointing device, and may have either a movable ora non-movable stick. The movable joystick operates similar to atrackball, except that a stick is inserted into the ball giving the usera means of grabbing the ball. The stick also limits movement of theball. The non-movable joystick utilizes pressure sensors encircling thestick to sense the force and direction in which the user is pushing thestick. Thus, the non-movable joystick does not communicate a position tothe computer, instead it senses a force vector which the computer mayuse to adjust the position of a screen object. With either type ofjoystick, manipulation of the switches and stick is very difficult withonly one hand, thus, in order to use a joystick, the user must removeboth hands from the keyboard.

Eyetracking devices use expensive, sophisticated methods of determiningwhere on the computer screen the user's eyes are focused. In this waythe user's hands do not have to leave the keyboard in order for thepositional information to be communicated to the computer.Unfortunately, however, this technology is not within financial reach ofmost computer users.

Touch screens permit the user to communicate a position to the computerby actually touching an area on the computer screen. Usually the screenarea is associated with an object or menu choice displayed on thescreen. As with all of the aforementioned pointing devices, with theexception of the eyetracking devices, the user's hand must leave thekeyboard to use the device.

From the foregoing, it can be seen that it would be quite desirable toprovide a method of communicating an object's position to the computerwhich does not require the removal of either of the user's hands fromthe keyboard and which may be economically produced. It is accordinglyan object of the present invention to provide such a method andassociated apparatus.

SUMMARY OF THE INVENTION

In carrying out the principles of the present invention, in accordancewith an embodiment thereof, a method is provided which permits the userto communicate positional information to the computer by obstructing alight grid with the user's finger, without removing either of the user'shands from the keyboard. An apparatus is also provided which producesthe light grid from a single light source and detects the position of anobject obstructing the grid.

In broad terms, a method of sensing an object's position is provided,the method comprising the steps of generating a light beam havingsubstantially parallel sides, converting the light beam to anoscillating beacon, the oscillating beacon having first and seconddifferently directed portions, the first and second beacon portionsbeing disposed in a first plane, intercepting and reflecting at leastone of the first and second oscillating beacon portions in the firstplane, transposing at least one of the first and second beacon portionsto a second plane, the second plane being offset from the first plane,interposing the object in the path of at least one of the first andsecond beacon portions to interrupt it, sensing the interruption of atleast one of the first and second beacon portions in the second plane,and utilizing the sensed interruption to determine the position of theinterposed object in the second plane.

An optical digitizer is also provided, the optical digitizer including alight source, the light source producing a beam of light, a beacongenerator, the beacon generator producing a beacon from the beam oflight, the beacon including a first beacon portion, a first reflector,the first reflector reflecting the first beacon portion, and a firstlight pipe, the first light pipe transposing the first beacon portionsuch that the transposed first beacon portion does not intersect thereflected first beacon portion.

Additionally, a computer keyboard device of the type having a generallyplanar keypad with a plurality of keys disposed on a top surfacethereof, a housing supporting the keypad, and further having thecapability of detecting the position of an object is provided, thecomputer keyboard device comprising reflector means, the reflector meansbeing mounted intermediate the keypad and the housing, beacon producingmeans, the beacon producing means being mounted intermediate the keypadand the housing, and being positioned so that a beacon of light isdirected to sweep repeatedly across the reflector means to produce areflected light beacon in a first plane, beacon transposing means fortransposing the reflected light beacon to a second plane, and lightsensing means for measuring the intensity of light received therein, thelight sensing means being positioned to receive the transposed andreflected light beacon therein.

The use of the disclosed method and associated apparatus enablespositional information to be conveniently and economically communicatedto the computer. Use of the computer keyboard device embodiment enablesthe user's time to be more effectively utilized since the user's handsdo not have to leave the keyboard to communicate positional informationto the computer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an optical digitizer embodyingprinciples of the present invention;

FIG. 2 is a flow chart illustrating a method of determining an object'sposition embodying principles of the present invention.

FIG. 3 is a top plan view of a computer keyboard having the opticaldigitizer of FIG. 1 thereon;

FIG. 4 is a cross-sectional view through the keyboard, taken along line4--4 of FIG. 3;

FIG. 5 is an isometric view of a light grid produced by the opticaldigitizer illustrating obstructed and unobstructed portions of the lightgrid;

FIG. 6A is a plot of light reflected back to a light sensor of theoptical digitizer when the light grid is totally unobstructed;

FIG. 6B is a plot of the light reflected when the light grid isobstructed by an object in a first position;

FIG. 6C is a plot of the light reflected when the light grid isobstructed by an object in a second position;

FIG. 6D is a plot of the light reflected when the light grid isobstructed by an object in a third position;

FIG. 6E is a plot of the light reflected when the light grid isobstructed by an object in a fourth position;

FIG. 7 is a schematic representation of another optical digitizerembodying principles of the present invention;

FIG. 8 is a cross-sectional view through the optical digitizer of FIG.7, taken along line 8--8 of FIG. 7;

FIG. 9 is a top plan view of a partially cut away computer keyboardhaving the optical digitizer of FIG. 7 thereon;

FIG. 10 is a schematic representation of yet another optical digitizerembodying principles of the present invention; and

FIG. 11 is a top plan view of a partially cut away computer keyboardhaving the optical digitizer of FIG. 10 thereon.

DETAILED DESCRIPTION

Illustrated in FIG. 1 is an optical digitizer 10 which embodiesprinciples of the present invention. It is shown in highly schematicizedform for the purpose of clarity. Dashed lines and arrows are used torepresent paths and directions, respectively, of light. Filledarrowheads represent directions of unreflected light and unfilledarrowheads represent directions of reflected light in a manner that willbecome apparent as the following detailed description is read andunderstood.

A light source 12 provides a compact beam of light 14 which is in theinfrared portion of the light spectrum in the illustrated preferredembodiment. The light source 12 includes a laser 16 which, in turn,includes a light emitting diode 20 and a collimator 22. The lightemitting diode 20 produces infrared light when leads 18 are connected toa power source (not shown). The infrared light produced by the lightemitting diode 20 is made into the beam 14 having essentially parallelsides by the collimator 22.

The beam 14 next passes into a beam splitter 24. The beam splitter 24includes a half-silvered mirror 26 which passes half of the beam 14 andreflects the other half. The reflected half of the beam 14 is not usedin the illustrated preferred embodiment, so it is not shown in FIG. 1.

The beam 14 next passes into a beacon generator 28. The beacon generator28 produces a beacon 30 from the beam 14 by reflecting the beam 14 offof an oscillating mirror 32. The beacon 30 differs from the beam 14 inthat the beacon 30 "sweeps" across a plane, whereas the beam 14 remainsstationary. In other words, the beacon 30 is the beam 14 put into motionby the oscillating mirror 32.

It is to be understood that the beacon 30 may be generated from the beam14 by another method without deviating from the principles of thepresent invention. For example, instead of the oscillating mirror 32 inthe beacon generator 28, a rotating polygonal mirror could be used torepeatedly and sequentially sweep beam 14 across an area. As a furtherexample, beam 14 could be directed across a curved surface instead of aflat plane.

The beacon 30 is directed into a beacon separator 34. In the beaconseparator 34, the beacon 30 is separated into several components. Onecomponent is (as viewed in FIG. 1) a horizontal component 36. Thehorizontal component 36 passes through the beacon separator 34 in theillustrated preferred embodiment without any change in direction.Another component, a vertical component 38 (as viewed in FIG. 1), isreflected off of a mirror 40 so that it is directed in a directiondifferent from the horizontal component 36.

In the area intermediate the horizontal component 36 and the verticalcomponent 38 of the beacon 30 in the beacon separator 34 is adiscriminating reflector 42. The purpose of the discriminating reflector42 is to allow the optical digitizer 10 to discriminate the horizontalcomponent 36 from the vertical component 38. The discriminatingreflector 42 directs a small portion of the beacon 30 back to theoscillating mirror 32. The manner in which the discriminating reflector42 allows discrimination between the horizontal and vertical components36,38 will become clear upon further description of the preferredembodiment below.

The horizontal component 36 of the beacon 30 next strikes a reflector 44which directs the beacon 30 in a downward direction as viewed in FIG. 1.Thus, it can be seen that as the horizontal component 36 of the beacon30 sweeps across the downwardly facing surface of reflector 44, it ismade to sweep horizontally from side to side as viewed in FIG. 1. Theuppermost limit of the horizontal component 36, illustrated as a beam 46in the beacon separator 34, once reflected off of the reflector 44,becomes the leftmost limit of a horizontal beacon portion 48 as viewedin FIG. 1. The lowermost limit of the horizontal component 36,illustrated as a beam 50, once reflected off of the reflector 44,becomes the rightmost limit of the horizontal beacon portion 48 asviewed in FIG. 1. Therefore, the horizontal beacon portion 48 is nothingmore than the horizontal component 36 of the beacon 30 reflected off ofthe reflector 44.

The reflector 44 in the illustrated preferred embodiment is constructedof a material which enhances the accuracy of the optical digitizer 10.The material, a reflective angle film (RAF) available from the 3MCorporation, reflects light at the same angle independent of the angleat which the light strikes its surface, within limits. In FIG. 1, it canbe seen that beam 46 strikes the reflector 44 (constructed of the RAFmaterial) at a slightly different angle than does beam 50, however, oncereflected off of reflector 44, beams 46 and 50 are parallel in thehorizontal beacon portion 48. It is to be understood that, in carryingout the principles of the present invention, the reflector 44 does nothave to be made of the RAF material, and that beams 46 and 50 do nothave to be parallel in the horizontal beacon portion 48.

In keeping with the principles of the present invention, the reflector44 could have a curved shape instead of the linear shaperepresentatively illustrated in FIG. 1. In that way, a beam passing overthe surface of the reflector 44 could be reflected in a direction whichdepends upon the curvature of the reflector 44.

Vertical component 38 of the beacon 30, after leaving the mirror 40 inthe beacon separator 34, strikes a reflector 52 which is made of the RAFmaterial in the illustrated preferred embodiment. A beam 54, farthest tothe right in the vertical component 38 as illustrated in FIG. 1, strikesthe reflector 52 and is reflected to the right in a direction orthogonalto the horizontal beacon portion 48. A beam 56, farthest to the left inthe vertical component 38, strikes the reflector 52 and is also directedto the right, orthogonal to horizontal beacon portion 48 as illustratedin FIG. 1. Thus, it can be seen that vertical component 38 of the beacon30 is reflected off of reflector 52 so that it sweeps vertically, asillustrated in FIG. 1, between the representatively shown beams 54 and56, forming a vertical beacon portion 58 which is orthogonal tohorizontal beacon portion 48. Note that, as with reflector 44 describedabove, reflector 52 could have a curved shape and could be made of othermaterials without deviating from the principles of the presentinvention.

Since beam 14 is continuously directed to the oscillating mirror 32 inthe beacon generator 28, the resulting beacon 30 is also continuous.Therefore, although beams 46 and 50 are illustrated as being at theouter limits of horizontal beacon portion 48, and beams 54 and 56 areillustrated as being at the outer limits of vertical beacon portion 58,it is important to understand that the beam 14, in the form of thevertical or horizontal beacon portion 48,58 sweeps continuously betweenthese outer limits. Note, however, that at any one instant in theillustrated preferred embodiment, beam 14 may be directed to thehorizontal beacon portion 48 or vertical beacon portion 58, but notboth.

It is also important to note at this point that although separate beams46,50,54,56 are referred to in this description of the illustratedpreferred embodiment, no two of these are present at one time, sincethey all emanate from the same beam 14 produced by the light source 12.Beams 46,50,54,56 representatively illustrated in FIG. 1 are all simplydifferent positions of beam 14. Likewise, different beacon portions48,58 and beacon components 36,38 are just parts of beacon 30, which is,in turn, made up of different positions of beam 14 produced by theoscillating mirror 32.

Beam 56 intersects beam 46 at point 60 and intersects beam 50 at point62. Beam 54 intersects beam 46 at point 64 and intersects beam 50 atpoint 66. Since the horizontal beacon portion 48 is orthogonal to thevertical beacon portion 58, points 60, 62, 64, and 66 define the cornersof a rectangular light grid 68. In this light grid 68, the horizontalbeacon portion 48 sweeps from side to side, and the vertical beaconportion 58 sweeps from top to bottom, as representatively illustrated inFIG. 1. For the purpose of further description of the illustratedpreferred embodiment, the defined beginning of the sweep of thehorizontal beacon portion 48 shall be at its leftmost limit (beam 46 asillustrated in FIG. 1), and the defined beginning of the sweep of thevertical beacon portion 58 shall be at its upper limit (beam 56 asillustrated in FIG. 1).

It is to be understood that the light grid 68 could have a shape otherthan rectangular without deviating from the principles of the presentinvention. If, as described above, beams 46 and 50 are not parallel toeach other, a trapezoid shape is produced. If, additionally, beams 56and 54 are not parallel to each other, another polygonal shape isproduced. Light grid 68 may take virtually any shape in keeping with theprinciples of the present invention as long as no beam in the horizontalbeacon portion 48 is collinear with a beam in the vertical beaconportion 58.

Reflector 70, representatively illustrated in FIG. 1 as beinghorizontally disposed at the lowermost extent of horizontal beaconportion 48, reflects the horizontal beacon portion 48 directly back inthe direction of reflector 44. Unfilled arrowheads on beamsrepresentatively illustrated in horizontal beacon portion 48 indicatethe direction of beams which have reflected off of reflector 70. Thus,beams in the horizontal beacon portion 48 are reflected back toreflector 44, thence back through the beacon separator 34 to theoscillating mirror 32 in the beacon generator 28, and thence to the beamsplitter 24.

In a similar manner, reflector 72, representatively illustrated in FIG.1 as being vertically disposed at the right-hand edge of vertical beaconportion 58, reflects the vertical beacon portion 58 directly back in thedirection of reflector 52. Unfilled arrowheads on beams representativelyillustrated in vertical beacon portion 58 indicate the direction ofbeams which have reflected off of reflector 72. Thus, beams in thevertical beacon portion 58 are reflected back to reflector 52, thenceback to the mirror 40 in the beacon separator 34, thence to theoscillating mirror 32 in the beacon generator 28, and thence to the beamsplitter 24.

Reflectors 70 and 72, in the illustrated preferred embodiment, are madeof a material which reflects light back in the same direction at whichit initially strikes the material. It is known to those skilled in theart as retro-reflecting film. There are several types ofretro-reflecting film, including micro corner cube and micro sphere.Applicants have found the micro corner cube type to give acceptableresults in the illustrated preferred embodiment apparatus.

In the illustrated preferred embodiment, with no obstruction blockingthe path of any beam, the cumulative total of the beams reflected backfrom the horizontal and vertical beacon portions 48,58 and thediscriminating reflector 42 to the beam splitter 24 is continuous andequal to the beam 14 which leaves the beam splitter 24 to enter thebeacon generator 28 (see FIG. 6A and accompanying description). It is tobe understood, however, that as beam 14 is reflected off of varioussurfaces and passes through various components of the illustratedpreferred embodiment, transmission errors and various inefficiencies inreflecting the beam 14 will result in a loss in light intensity by thetime it is reflected back to the beam splitter 24.

Discriminating reflector 42 in the beacon separator 34 takes advantageof the above-mentioned loss in light intensity by reflecting a smallportion of the beacon 30 back to the beam splitter 24 before it reflectsoff of any of the other reflecting surfaces 40,44,52,70,72. Thisproduces a momentary increase in light intensity reflected back to thebeam splitter 24 to aid in discriminating between the horizontal andvertical components 36,38 of the beacon 30 reflected back to the beamsplitter 24. Other methods of discrimination may be utilized withoutdeviating from the principles of the present invention. For example, anonreflective surface could be provided in place of discriminatingreflector 42, which would produce an absence of reflected light betweenthe horizontal and vertical components 36,38 reflected back to the beamsplitter 24. Alternatively, a series of coded nonreflecting lines couldbe positioned near the ends of the reflectors 70,72, the code tellingthe computer that a horizontal and/or vertical sweep has ended and/orbegun. Yet another method of telling a horizontal from a vertical sweepwould be to provide an encoder on the oscillating mirror 32 so that themirror's position and, therefore, the direction of the beam 14 iscommunicated to the computer.

The reflected beam 14, representatively illustrated in FIG. 1 having anunfilled arrowhead, enters the beam splitter 24 and strikes thehalf-silvered mirror 26. A portion of the reflected beam 14 is directedto a light sensor 74. A photodiode 76 in the path of the reflected beam14 is capable of measuring the beam's intensity. The photodiode 76 hasleads 78 for connecting to measurement electronics (not shown). Othermethods of measuring the beam's intensity may be used without deviatingfrom the principles of the present invention. Use of the preferredembodiment apparatus illustrated in FIG. 1, and the resultingmeasurements of the intensity of the reflected beam 14 over time, allowthe position of an object in the light grid 68 to be determined.

Turning now to FIG. 2, a preferred embodiment of a method 150 ofdetermining an object's position in accordance with the principles ofthe present invention is representatively illustrated. The preferredmethod embodiment is for determining the object's position on atwo-dimensional plane, although other embodiments of the presentinvention may be used to determine the object's position in one or threedimensions, the object's velocity or acceleration, etc.

Commencing with step 152, a light beam is generated. Preferably, thelight beam is compact and is composed of light rays which areessentially parallel to each other. The more compact the light beam, thegreater the resolution capability, and the more the light rays areparallel to each other, the greater the accuracy of the preferredembodiment method 150.

Through testing, applicants have found that a conventional lightemitting diode-type infrared laser having an integral collimatorproduces a suitable light beam for use with the preferred embodimentmethod 150. Other suitable light beam producers are commerciallyavailable, for example, a laser of the type typically used in compactdisk drives. It is not necessary that the light beam produced be in theinfrared range of the light spectrum.

Continuing with step 154, the beam is passed through a beam splitter.The purpose of the beam splitter in the preferred embodiment method 150is to separate the light which is later reflected back to the beamsplitter from the light beam produced in step 152. The preferredembodiment method 150 utilizes a half-silvered mirror which passes fiftypercent of the light beam, and reflects fifty percent of the light beam.Other beam splitter configurations suitable for use with the preferredembodiment method 150 are commercially available, such as a dual prismhaving a partially-reflective film between the prisms.

In the preferred embodiment method 150, the fifty percent of the lightbeam produced in step 152 which is reflected by the beam splitter is notutilized. It is to be understood, however, that this reflected fiftypercent of the light beam could be utilized to, for example, produce abeacon as described hereinbelow for use in determining an object'sposition, without deviating from the principles of the presentinvention.

Continuing with step 156, a beacon is produced from the unreflectedfifty percent of the light beam which is passed through the beamsplitter. In the preferred embodiment method 150, an oscillating mirroris used to reflect the beam back and forth repeatedly, thereby producingthe beacon. The oscillating mirror is also used later in the preferredembodiment method 150 to reflect the beacon produced in this step backto the beam splitter.

Other beacon producing means are suitable for use in the preferredembodiment method 150, for example, a rotating polygonal mirror. In somerespects, a rotating mirror has advantages over the oscillating mirror.For example, a rotating mirror produces a beacon which sweeps over anarea repeatedly in only one direction, instead of back and forth, makingit somewhat less complex to later differentiate between the forward andbackward sweeps. Another advantage of a rotating mirror is that ittypically produces a linear sweep rate, that is, the beam is made tosweep over an area with a relatively constant angular velocity, makingit somewhat less complex to later compute the relationship between thebeam's position and time. In comparison, the oscillating mirrortypically produces a sinusoidal sweep rate. Applicants, however, havechosen to use the oscillating mirror in the preferred embodiment method150 because it has less bulk and fewer moving parts than a typicalrotating mirror.

Continuing with step 158, the beacon produced in step 156 is separatedinto two beacon portions. Each of the beacon portions so separated isused later to determine the object's position in one dimension.Therefore, two beacon portions are needed in the preferred embodimentmethod 150, since the object's position is to be determined in twodimensions.

In the preferred embodiment method 150, applicants utilize a beaconseparator in step 158 which has a reflective surface partially extendinginto the area swept by the beacon produced in step 156. The reflectivesurface diverts a portion of the beacon so that it may, separately fromthe undiverted portion of the beacon, be swept across thetwo-dimensional plane in which the object's position is to bedetermined. Other means of separating the beacon into multiple portions,for example a prism, may be utilized without deviating from theprinciples of the present invention.

Continuing with step 160, the two beacon portions separated in step 158are swept over an area in which the position of the object is to bedetermined. In the preferred embodiment method 150, the area is thetwo-dimensional plane discussed above. Preferably, the two beaconportions are swept over the area such that the beacon portions areorthogonal to each other. In this manner, later computations of theobject's position are somewhat less complex. It is to be understood,however, that it is not necessary, in keeping with the principles of thepresent invention, for the beacon portions to be orthogonal to eachother when being swept over the area in which the position of the objectis to be determined.

To direct the beacon portions over the two-dimensional plane such thatthey are orthogonal to each other, applicants reflect each beaconportion off of a reflective surface having the property that thereflected beacon portion leaves the reflective surface at a relativelyconstant angle regardless the angle at which the beacon portion strikesthe reflective surface. Thus, the angle of one beacon portion leavingone reflective surface may be positioned so that it is orthogonal to theother beacon portion leaving the other reflective surface.

Other means may be utilized to direct the beacon portions orthogonallyover the two-dimensional plane without deviating from the principles ofthe present invention. For example, each beacon portion could bereflected off of a curved reflector having a curvature such that thebeacon portion would be reflected in the same direction no matter wherethe beacon portion strikes the curved reflector.

Continuing with step 162, after being swept over the area in which theposition of the object is to be determined, the beacon portions arereflected back to the beam splitter. The object, being positioned in thetwo-dimensional plane swept by the beacon portions, obstructs a fragmentof each beacon portion, thus preventing its reflection back to the beamsplitter.

For reflecting each beacon portion back to the beam splitter, applicantsutilize a reflective surface having the property that it reflects lightback in the same direction at which the light strikes the reflectivesurface. Other means, such as a mirror, may be utilized for reflectingeach beacon portion back to the beam splitter without deviating from theprinciples of the present invention.

Note that, in this step 162 of the preferred embodiment method 150, thebeacon portions are reflected back off of each reflective surface in adirection opposite to that which they had reflected off those reflectivesurfaces in the previous steps, namely, the reflective surfaces utilizedby applicants to orient the beacon portions orthogonally described instep 160 above, the reflective surface utilized by applicants in thebeacon separator described in step 158 above (only the beacon portiondiverted in step 158), and the oscillating mirror utilized by applicantsfor producing the beacon as described in step 156 above.

Continuing with step 164, the beacon portions reflected back to the beamsplitter in step 162 are directed to a light sensor. The light sensormeasures the intensity of the beacon portions reflected back to the beamsplitter.

Applicants utilize a photodiode suitable for measuring the intensity ofinfrared light to measure the intensity of the beacon portions reflectedback to the beam splitter. Other light sensors may be used withoutdeviating from the principles of the present invention. It is to beunderstood, however, that the light sensor must be capable of measuringthe intensity of the light produced in step 152 and must be capable ofdetecting the unreflected fragments of the beacon portions, describedabove in regard to step 162.

Continuing with step 166, the object's position in the two-dimensionalplane is determined. In the preferred embodiment method 150, theunreflected fragments of the beacon portions, detected in step 164above, indicate the position of the object, since the object causedthose fragments to not be reflected back to the beam splitter in step162 above.

One unreflected fragment will be present in each beacon portionreflected back to the beam splitter in the preferred embodiment method150. By computing the position of the unreflected fragment in eachbeacon portion, the position of the object in each of two dimensions canbe determined.

Applicants utilize a microprocessor to time the unreflected fragment ineach beacon portion and compute the object's position, based on thesinusoidal sweep rate of the oscillating mirror. Since, in the preferredembodiment method 150, the beacon portions are orthogonal to each other,the object's position can be directly computed in Cartesian coordinatesin the two-dimensional plane. If, however, the beacon portions are notorthogonal to each other, the object's cartesian coordinates can stillbe computed, albeit using more complex calculations, without deviatingfrom the principles of the present invention.

Turning now to FIG. 3, the optical digitizer 10 is representativelyillustrated as being disposed on a computer keyboard 80 having keys 90.The keyboard 80 is otherwise conventional, suited for input of text bytyping on keys 90, and is typically used in conjunction with a computer.

As representatively illustrated in FIG. 3, the top surface of thekeyboard 80 having the keys 90 thereon is in a vertical orientation,with the side which typically faces the user being at the bottom of theillustration. It is to be understood that, in the following description,the use of the terms "vertical" and "horizontal" refer to therepresentatively illustrated orientation of the keyboard 80 in FIG. 3.Stated in another manner, the "vertical" direction runs up and down, andthe "horizontal" direction runs side to side in FIG. 3.

Light source 12, beam splitter 24, beacon generator 28, beacon separator34, and light sensor 74 (combinatively forming the previously describedoptical digitizer 10) are shown in schematicized form, convenientlymounted near the upper left-hand portion of the keyboard 80, althoughother positionings of these elements are possible without deviating fromthe principles of the present invention.

Reflector 44 is mounted on a support 82 to the rear of the keys 90.Reflector 72 is mounted on a support 84 to the right of the keys 90.Reflector 52 is mounted on a support 86 to the left of the keys 90.Reflector 70 is mounted on an upwardly extending and rearwardly facingportion of a space bar 88.

Points 60,62,64,66 form the corners of the rectangular light grid 68. Atthe light grid's horizontal extremities are beams 46 and 50. At thelight grid's vertical extremities are beams 54 and 56. Thus, in theillustrated preferred embodiment, the light grid 68 is positioned over aportion of the keys 90. In keeping with the principles of the presentinvention, the light grid 68 may be enlarged or reduced to anyconvenient size or shape and may overlay all, a portion of, or none ofthe keys 90.

Illustrated in FIG. 4 is a cross-sectional view taken along line 4--4through the keyboard 80 illustrated in FIG. 3. In this view, the spacingbetween the keys 90 and the beam 50 can be seen. Reflectors 44 and 70are positioned just above the keys 90, reflector 44 being mounted tosupport 82, and reflector 70 being mounted to the space bar 88.

Positioning the optical digitizer 10 in this manner allows a computeruser to operate the digitizer 10 without removing the user's hands fromthe keyboard 80. The user can conveniently lift the fingers slightlyabove the keyboard 80, activate the optical digitizer 10 by, forexample, pressing an appropriate control or function key on thekeyboard, and then use one finger to obstruct the light grid 68 andthereby communicate positional information, select a screen object, etc.When the user is finished using the digitizer 10, it is deactivated by,for example, pressing another control or function key, and the user maytype on the keys 90 again. This is all accomplished without the user'shands leaving their normal positions above the keyboard 80.

FIG. 5 shows how the location of an obstruction 92 in the light grid 68is determined. As in the above described figures, filled arrowheadsindicate the direction of light beams which have not been reflected offof reflector 70 or 72, while blank arrowheads indicate the direction ofbeams which have been reflected off of reflector 70 or 72. Note that inFIG. 5, beams 56,50,54, and 46, and points 60,62,64, and 66 correspondto the same beams and points in FIGS. 1,3, and 4.

Beams 46 and 50, at the outer limits of the horizontal beacon portion 48are seen to be reflected off of reflector 70. They will be detected, asdescribed above, by the light sensor 74. Likewise, beams 94 and 96,passing just to each side of the obstruction 92 are also reflected backto the light sensor 74. However, beam 98, which strikes the obstruction92 is not reflected back and, therefore, cannot be detected by the lightsensor 74. Note that each of beams 46,50,94,96, and 98 are part of thehorizontal beacon portion 48. Thus, the absence of a beam beingreflected back from the horizontal beacon portion 48 is detected by thelight sensor 74. The center of the horizontal position of theobstruction 92 can be determined by averaging the horizontal positionsof beams 94 and 96 which pass just to each side of the obstruction 92.

The vertical portion of the grid 68 operates in the same manner as thehorizontal portion. Beams 54 and 56, at the outer limits of the verticalbeacon portion 58 are seen to be reflected off of reflector 72. Theywill be detected, as described above, by the light sensor 74. Likewise,beams 100 and 102, passing just to each side of the obstruction 92 arealso reflected back to the light sensor 74. However, beam 104, whichstrikes the obstruction 92 is not reflected back and, therefore, cannotbe detected by the light sensor 74. Note that each of beams54,56,100,102, and 104 are part of the vertical beacon portion 58. Thus,the absence of a beam being reflected back from the vertical beaconportion 58 is detected by the light sensor 74. The center of thevertical position of the obstruction 92 can be determined by averagingthe vertical positions of beams 100 and 102 which pass just to each sideof the obstruction 92.

FIGS. 6A through 6E representatively illustrate how the light sensor 74receives and measures the intensity of the reflected beam 14. Thevertical scale in each of FIGS. 6A through 6E is reflected lightintensity which the photodiode 76, through leads 78, communicates to thecomputer. The horizontal scale is time. Traces on these graphs thusindicate a "snapshot" in time of the reflected light intensity "seen" bythe light sensor 74.

FIG. 6A representatively illustrates what the light sensor 74 sees whenthere is no obstruction in the light grid 68. Trace 106 is completelyflat (with the exception of small increases in intensity 108 betweenhorizontal and vertical sweeps of the beacon 30), indicating that all ofthe beam 14 from the horizontal and vertical beacon portions 48,58 isbeing reflected back off of reflectors 70 and 72.

The small increases in intensity 108 between the horizontal and verticalsweeps are due to the portion of the beacon 30 reflected back to thelight sensor 74 by the discriminating reflector 42 in the beaconseparator 34. In this manner, the computer can discriminate between avertical and a horizontal sweep. If, as described above, a nonreflectivesurface is used to discriminate between horizontal and vertical sweepsof the beacon 30, a decrease, instead of an increase 108, in lightintensity would be seen by the light sensor 74.

Note that in FIG. 6A a vertical sweep of the beacon 30 is followed byanother vertical sweep and a horizontal sweep is followed by anotherhorizontal sweep. This is due to the fact that the mirror 32 isoscillating. Each sweep is immediately repeated in reverse as the mirror32 oscillates back and forth. If a rotating polygonal mirror is usedinstead of an oscillating mirror, a vertical sweep will be followed by ahorizontal sweep and a horizontal sweep will be followed by a verticalsweep.

FIG. 6B representatively illustrates a trace 110 produced when there isan obstruction 92 in the light grid 68 near the beginning of bothhorizontal and vertical sweeps. Referring to FIG. 5, the obstruction 92would be located near point 60, but still within the light grid 68.

At the beginning of the horizontal sweep, the light intensityrepresented by trace 110 is the same as trace 106 in the previous FIG.6A. As the horizontal beacon portion 48 is reflected back to the lightsensor 74, between beams 46 and 94, the reflected light intensityremains the same (portion 112 of trace 110). Where the horizontal beaconportion 48 is not reflected back to the light sensor 74, such as beam 98between beams 94 and 96, the reflected light intensity drops (portion116 of trace 110). Between beams 96 and 50, when the horizontal beaconportion 48 is again reflected back to the light sensor 74, the reflectedlight intensity returns to its initial level (portion 114 of trace 110).An increase in light intensity 108 indicates the beginning of thevertical sweep.

As with the horizontal sweep described above, at the beginning of thevertical sweep, the light intensity represented by trace 110 is the sameas trace 106. As the vertical beacon portion 58 is reflected back to thelight sensor 74, between beams 56 and 100, the reflected light intensityremains the same (portion 118 of trace 110). Where the vertical beaconportion 58 is not reflected back to the light sensor 74, such as beam104 between beams 100 and 102, the reflected light intensity drops(portion 120 of trace 110). Between beams 102 and 54, when the verticalbeacon portion 58 is again reflected back to the light sensor 74, thereflected light intensity returns to its initial level (portion 122 oftrace 110). The remainder of trace 110 is the reverse of that describedimmediately above as the mirror 32 oscillates back to its initialposition to begin another sweep of the beacon 30.

Thus, it is seen that a drop in reflected light intensity is seen by thelight sensor 74 when an obstruction 92 is encountered in the horizontaland vertical sweeps. The center of the obstruction's position may becalculated by measuring the time from the beginning of the horizontaland vertical sweeps to the centers of the drops in reflected lightintensity (portions 116 and 120 of trace 110). The times thus measuredcorrespond to the horizontal and vertical positions of the obstruction92 in the light grid 68.

The relationship between time and horizontal and vertical positionwithin the light grid 68 will vary, depending on many factors. If, forexample, the position of the oscillating mirror 32 varies according to asinusoidal function, the relationship between time and horizontal andvertical position within the light grid 68 will also be a nonlinearfunction. If the beams which make up the horizontal or vertical beaconportion 48,58 are not parallel to each other, or if the beacon portionsare not orthogonal to each other, the relationship between time andposition will be affected accordingly.

FIG. 6C is similar to FIG. 6B, except that the representativelyillustrated portions of a trace 124 indicating a reduced reflected lightintensity 126,128 are near the end of the horizontal and verticalsweeps, respectively. Referring to FIG. 5, the trace 124 corresponds toa position of the obstruction 92 near point 66, but still within thelight grid 68. Note that, with the obstruction 92 in that position, theunreflected beam 98 in the horizontal beacon portion 48 would be nearthe end of the horizontal sweep, corresponding to portion 126 of trace124, and that the unreflected beam 104 in the vertical beacon portion 58would be near the end of the vertical sweep, corresponding to portion128 of trace 124.

Representatively illustrated in FIG. 6D are portions of a trace 130having reduced reflected light intensity 132,134 near the beginning ofthe horizontal sweep and near the end of the vertical sweep of thebeacon 30. This corresponds to a position of the obstruction 92 nearpoint 64, but still within the light grid 68 (see FIG. 5).

Representatively illustrated in FIG. 6E are portions of a trace 136having reduced reflected light intensity 138,140 near the end of thehorizontal sweep and near the beginning of the vertical sweep of thebeacon 30. This corresponds to a position of the obstruction 92 nearpoint 62, but still within the light grid 68 (see FIG. 5).

Thus, a person of ordinary skill in the art, given the characteristicsof the optical digitizer 10 and the reflected light intensity detectedover time by the light sensor 74, is able to determine the position ofan obstruction 92 anywhere within the light grid 68.

Up to this point, the optical digitizer 10 has been described withoutregard to the relationship between a plane across which the horizontalbeacon portion 48 is swept and a plane across which the vertical beacon58 portion is swept. FIGS. 1,3, and 5 illustrate preferred embodimentsin which the above described planes are coplanar. If, however, theplanes are not coplanar, the optical digitizer 10 functions as describedhereinabove, but the obstruction 92 is then permitted to obstruct one ofthe beacon portions 48,58 without obstructing the other. It is thenpossible to perform other functions, for example, measure the velocityof the obstruction 92 by dividing the distance separating the planesswept by the horizontal and vertical beacon portions 48,58 by thedifference in time between when the light sensor 74 sees a reducedreflected light intensity in each sweep.

It is also possible to determine the position of an obstruction in moreor less than two dimensions using the principles of the presentinvention. If only one spatial dimension is desired, then only onebeacon portion is needed. If three spatial dimensions are desired, morethan one optical digitizer 10 may be stacked to form a three-dimensionallight grid.

Illustrated in FIG. 7 is another preferred embodiment of an opticaldigitizer 200 which embodies principles of the present invention. It isshown in highly schematicized form for the purpose of clarity. Dashedlines and arrows are used to represent paths and directions,respectively, of light. Filled arrowheads represent directions ofunreflected light and unfilled arrowheads represent directions ofreflected light in a manner similar to that used in FIGS. 1, 3, 4, and5. In the optical digitizer 200 illustrated in FIG. 7, however, light isreflected in more than one plane.

A light source 202 provides a compact beam of light 204 which is in theinfrared portion of the light spectrum in the illustrated preferredembodiment. The light source 202 includes a laser 206 which, in turn,includes a light emitting diode 208 and a collimator 210. The lightemitting diode 208 produces infrared light. The infrared light producedby the light emitting diode 208 is made into the beam 204 havingessentially parallel sides by the collimator 210.

The beam 204 next passes through a half-silvered mirror 212 which passeshalf of the beam 204 and reflects the other half. The reflected half ofthe beam 204 is not used in the illustrated preferred embodiment, so itis not shown in FIG. 7. The half-silvered mirror 212 performsessentially the same function in the optical digitizer 200representatively illustrated in FIG. 7 as the half-silvered mirror 26 inthe beam splitter 24 illustrated in FIG. 1.

The beam 204 next passes through a refracting surface 214 and into asubstantially transparent and planar lightguide 215. The lightguide 215has a refractive index different than that of air, such that the beam204 changes direction as it passes through the refracting surface 214.Applicants' preferred material for the lightguide 215 is clear plastic,although other materials, for example, glass, may be used withoutdeparting from the principles of the present invention. The purpose ofthe refracting surface 214 in the illustrated optical digitizer 200 isto enhance packaging, i.e., to permit the light source 202,half-silvered mirror 212, etc., to be positioned for optimumcompactness.

The beam 204 next passes through the lightguide 215 to an oscillatingmirror 216. The beam 204 reflects off of the oscillating mirror 216,producing a beacon 218. The beacon 218 differs from the beam 204 in thatthe beacon 218 "sweeps" across a plane, whereas the beam 204 remainsstationary. In other words, the beacon 218 is the beam 204 put intomotion by the oscillating mirror 216.

It is to be understood that the beacon 218 may be generated from thebeam 204 by another method without deviating from the principles of thepresent invention. For example, instead of the oscillating mirror 216, arotating polygonal mirror could be used to repeatedly and sequentiallysweep beam 204 across an area. As a further example, beam 204 could bedirected across a curved surface instead of a flat plane.

The beacon 218 is directed by the oscillating mirror 216 to sweep acrosstwo parabolic mirrors formed on edges of the lightguide 215, one ofwhich 220 is oriented generally vertical as viewed in FIG. 7, and theother of which 222 is oriented generally horizontal as viewed in FIG. 7.A portion of the beacon 218, the "vertical" component 224 sweeps acrossthe vertical parabolic mirror 220. Likewise, a "horizontal" beaconcomponent 226 sweeps across the horizontal parabolic mirror 222. In amanner that will be readily appreciated by one of ordinary skill in theart, and which is described more fully hereinbelow, the horizontalcomponent 226 and horizontal parabolic mirror 222 are utilized todetermine an object's horizontal position within a light grid, and thevertical component 224 and vertical parabolic mirror 220 are utilized todetermine the object's vertical position within the light grid.

The horizontal parabolic mirror 222 in the illustrated optical digitizer200 has a smooth upwardly facing surface 234 with reflective material235, such as silver, applied thereto. The upwardly facing surface 234has a parabolic shape so that the radially-directed horizontal component226, once reflected off of the upwardly facing surface 234 will sweephorizontally as a beacon having parallel sides. The vertical parabolicmirror is similarly constructed so that the radially directed verticalcomponent 224, once reflected off of leftwardly facing surface 236, willsweep vertically as a beacon having parallel sides.

When the horizontal component 226 reflects off of the horizontalparabolic mirror 222, it is directed in an upward direction as viewed inFIG. 7. Thus, it can be seen that as the horizontal component 226 of thebeacon 218 sweeps across the upwardly facing surface 234 of horizontalparabolic mirror 222, it is made to sweep horizontally from side to sideas viewed in FIG. 7. The lowermost limit of the horizontal component226, illustrated as a beam 228, once reflected off of the horizontalparabolic mirror 222, becomes the leftmost limit of a horizontal beaconportion 230 as viewed in FIG. 7. The uppermost limit of the horizontalcomponent 226, illustrated as a beam 232, once reflected off of thehorizontal parabolic mirror 222, becomes the rightmost limit of thehorizontal beacon portion 230 as viewed in FIG. 7. Therefore, thehorizontal beacon portion 230 is nothing more than the horizontalcomponent 226 of the beacon 218 reflected off of the horizontalparabolic mirror 222.

In FIG. 7, it can be seen that beam 228 strikes the horizontal parabolicmirror 222 at a slightly different angle than does beam 232, however,once reflected off of horizontal parabolic mirror 222, beams 228 and 232are parallel in the horizontal beacon portion 230. It is to beunderstood that, in carrying out the principles of the presentinvention, the horizontal parabolic mirror 222 does not have to be anintegral portion of lightguide 215 or be silver-coated, and that beams228 and 232 do not have to be parallel in the horizontal beacon portion230. In keeping with the principles of the present invention, thehorizontal parabolic mirror 222 could have a shape other than parabolic.

Vertical component 224 of the beacon 218, after reflecting off theoscillating mirror 216, strikes the vertical parabolic mirror 220 whichis constructed in a manner similar to the horizontal parabolic mirror222 in the illustrated preferred embodiment. A beam 238, lowermost inthe vertical component 224 as illustrated in FIG. 7, strikes thevertical parabolic mirror 220 and is reflected to the left in adirection orthogonal to the horizontal beacon portion 230. A beam 240,uppermost in the vertical component 224, strikes the vertical parabolicmirror 220 and is also directed to the left, orthogonal to horizontalbeacon portion 230 as illustrated in FIG. 7. Thus, it can be seen thatvertical component 224 of the beacon 218 is reflected off of verticalparabolic mirror 220 so that it sweeps vertically, as illustrated inFIG. 7, between the representatively shown beams 238 and 240, forming avertical beacon portion 242 which is orthogonal to horizontal beaconportion 230. Note that, as with horizontal parabolic mirror 222described above, vertical parabolic mirror 220 could have a differentshape and could be made of other materials without deviating from theprinciples of the present invention.

Since beam 204 is continuously directed to the oscillating mirror 216,the resulting beacon 218 is also continuous. Therefore, although beams228 and 232 are illustrated as being at the outer limits of horizontalbeacon portion 230, and beams 238 and 240 are illustrated as being atthe outer limits of vertical beacon portion 242, it is important tounderstand that the beam 204, in the form of the vertical or horizontalbeacon portion 230,242 sweeps continuously between these outer limits.Note, however, that at any one instant in the illustrated preferredembodiment, beam 204 may be directed to the horizontal beacon portion230 or vertical beacon portion 242, but not both.

It is also important to note at this point that although separate beams228,232,238,240 are referred to in this description of the illustratedpreferred embodiment, no two of these are present at one time, sincethey all emanate from the same beam 204 produced by the light source202. Beams 228,232,238,240 representatively illustrated in FIG. 7 areall simply different positions of beam 204. Likewise, different beaconportions 230,242 and beacon components 224,226 are just parts of beacon218, which is, in turn, made up of different positions of beam 204produced by the oscillating mirror 216.

Beam 240 intersects beam 228 at point 244 and intersects beam 232 atpoint 246. Beam 238 intersects beam 228 at point 248 and intersects beam232 at point 250. Since the horizontal beacon portion 230 is orthogonalto the vertical beacon portion 242, points 244, 246, 248, and 250 definethe corners of a rectangular light grid 252. In this light grid 252, thehorizontal beacon portion 230 sweeps from side to side, and the verticalbeacon portion 242 sweeps from top to bottom, as representativelyillustrated in FIG. 7. For the purpose of further description of theillustrated preferred embodiment, the defined beginning of the sweep ofthe horizontal beacon portion 230 shall be at its leftmost limit (beam228 as illustrated in FIG. 7), and the defined beginning of the sweep ofthe vertical beacon portion 242 shall be at its lower limit (beam 238 asillustrated in FIG. 7).

It is to be understood that the light grid 252 could have a shape otherthan rectangular without deviating from the principles of the presentinvention. If, as described above, beams 228 and 232 are not parallel toeach other, a trapezoid shape is produced. If, additionally, beams 240and 238 are not parallel to each other, another polygonal shape isproduced. Light grid 252 may take virtually any shape in keeping withthe principles of the present invention as long as no beam in thehorizontal beacon portion 230 is collinear with a beam in the verticalbeacon portion 242.

In a unique manner more fully described hereinbelow, the horizontal andvertical beacon portions 230 and 242, and the light grid 252 definedthereby, are "transposed", that is, transferred to another plane,different from a plane in which the components of the optical digitizer200 heretofore described lie. Thus, the light source 202, half-silveredmirror 212, lightguide 215, oscillating mirror 216, horizontal parabolicmirror 222, and vertical parabolic mirror 220 all lie in a plane asrepresentatively illustrated in FIG. 7. The light beam 204 and some ofits permutations (vertical portion 242, horizontal portion 230, andlight grid 252), however, coexist on another, transposed, plane.

This transposition is accomplished by means of two light pipes, avertical light pipe 254 which transposes the vertical beacon portion242, and which is generally vertically oriented as shown in FIG. 7, anda horizontal light pipe 256 which transposes the horizontal beaconportion 230, and which is generally horizontally oriented as shown inFIG. 7. Vertical light pipe 254 takes the leftwardly directed verticalbeacon portion 242, transposes it, and directs it to the right as viewedin FIG. 7. Horizontal light pipe 256 takes the upwardly directedhorizontal beacon portion 230, transposes it, and directs it downward asviewed in FIG. 7. Light pipes 254 and 256 are described more fully belowin the detailed description accompanying FIG. 8.

After the horizontal beacon portion 230 has been transposed and directeddownward by the horizontal light pipe 256, as described above, reflector258, representatively illustrated in FIG. 7 as being horizontallydisposed at the lowermost extent of horizontal beacon portion 230,reflects the horizontal beacon portion 230 directly back in thedirection of horizontal light pipe 256 and thence downwardly back tohorizontal parabolic mirror 222. Unfilled arrowheads on beamsrepresentatively illustrated in horizontal beacon portion 230 indicatethe direction of beams which have reflected off of reflector 258. Thus,beams in the horizontal beacon portion 230 are reflected from thehorizontal light pipe 256 back through the lightguide 215 to horizontalparabolic mirror 222, through the lightguide 215 again to theoscillating mirror 216, through the lightguide 215 yet again, and thenceto the half-silvered mirror 212.

In a similar manner, reflector 260, representatively illustrated in FIG.7 as being vertically disposed at the right-hand edge of vertical beaconportion 242, reflects the vertical beacon portion 242 directly back inthe direction of vertical light pipe 254, through the lightguide 215,and thence back to vertical parabolic mirror 220. Unfilled arrowheads onbeams representatively illustrated in vertical beacon portion 242indicate the direction of beams which have reflected off of reflector260. Thus, beams in the vertical beacon portion 242 are reflected backthrough the lightguide 215 to vertical parabolic mirror 220, through thelightguide 215 again to the oscillating mirror 216, through thelightguide 215 yet again, and thence to the half-silvered mirror 212.

Reflectors 258 and 260, in the illustrated preferred embodiment, aremade of a material which reflects light back in the same direction atwhich it initially strikes the material. It is known to those skilled inthe art as retro-reflecting film. There are several types ofretro-reflecting film, including micro corner cube and micro sphere.Applicants have found the micro corner cube type to give acceptableresults in the illustrated preferred embodiment apparatus.

In the illustrated preferred embodiment, with no obstruction blockingthe path of any beam, the cumulative total of the beams reflected backfrom the horizontal and vertical beacon portions 230,242 is continuousand equal to the beam 204 which leaves the half-silvered mirror 212,with the exception of the portion which strikes the refractive surface214 between the horizontal and vertical parabolic mirrors 220,222. Thus,referring to FIGS. 6A-6E, the increased reflected light intensityportion 108 between successive vertical and horizontal sweeps,corresponds to that portion of beacon 218 which is directed back throughthe refractive surface 214 between beacon portions 224 and 226. It is tobe understood, however, that as beam 204 is reflected off of varioussurfaces and passes through various components of the illustratedpreferred embodiment, transmission errors and various inefficiencies inreflecting the beam 204 will result in a loss in light intensity by thetime it is reflected back to the half-silvered mirror 212. As with thepreviously described and illustrated optical digitizer 10, other methodsof discriminating between horizontal and vertical sweeps may be utilizedwithout departing from the principles of the present invention.

The reflected beam 204, representatively illustrated in FIG. 7 having anunfilled arrowhead, is reflected back off of the oscillating mirror 216,back through the lightguide 215, and strikes the half-silvered mirror212. A portion of the reflected beam 204 is directed to a photodiode 262in the path of the reflected beam 204, which is capable of measuring thebeam's intensity. Other methods of measuring the beam's intensity may beused without deviating from the principles of the present invention. Useof the preferred embodiment apparatus illustrated in FIG. 7, and theresulting measurements of the intensity of the reflected beam 204 overtime (see FIGS. 6A-6E), allow the position of an object in the lightgrid 252 to be determined as described hereinabove.

Turning now to FIG. 8, a cross-sectional view of the optical digitizer200 representatively illustrated in FIG. 7 is shown. For the purpose ofclarity, only one representative beam 240 is shown in this view. Thepath of this beam 240 will be described below so that a completeunderstanding may be had of the manner in which the light grid 252 (seeFIG. 7) is vertically transposed.

Beam 240 originates at the oscillating mirror 216 when beam 204 (seeFIG. 7) strikes the oscillating mirror 216 while it is directed towardthe vertical parabolic mirror 220. At this point, beam 240 is a portionof the vertical beacon component 224 (see FIG. 7). Beam 240 leaves theoscillating mirror 216, travels through the lightguide 215, strikes thevertical parabolic mirror 220, and is reflected back through thelightguide 215. At this point, beam 240 is a portion of the verticalbeacon portion 242 (see FIG. 7).

After being reflected off of the vertical parabolic mirror 220 andtraveling through lightguide 215, beam 240 enters the vertical lightpipe 254. The beam 240 first strikes and is reflected off of a rightangle reflector 264. The right angle reflector 264 directs the beam 240vertically upward as viewed in FIG. 8. Right angle reflector 264 may beconstructed of any suitable material, such as a conventional mirror,capable of reflecting the beam 240. Applicants' preferred material forthe right angle reflector 264 is silver-coated clear plastic.

Beam 240 travels upwardly after being reflected off of the right anglereflector 264 and strikes a reflector 266. Reflector 266 directs thebeam 240 horizontally to the right as viewed in FIG. 8. Reflector 266 isconstructed using a material commonly known to those skilled in the artas right-angle film. Right-angle film reflects light back at a ninetydegree included angle and is available from the 3M Corporation.

Beam 240 leaves reflector 266 and travels to the right as viewed in FIG.8, and passes in front of the horizontal light pipe 256, which isconstructed in a manner similar to the vertical light pipe 254 describedabove. As also described above, the horizontal beacon portion 230 (seeFIG. 7) is transposed and, as representatively illustrated, intersectsthe vertically transposed vertical beacon portion 242 (see FIG. 7).

As beam 240 passes in front of the horizontal light pipe 256, itintersects beam 228 (see FIG. 7) at point 244, at a corner of the lightgrid 252 (see FIG. 7). Likewise, beam 240 intersects beam 232 (see FIG.7) at point 246, at another corner of the light grid 252. The beam 240continues traveling to the right until it strikes vertical reflector260.

Beam 240 reflects off of reflector 260 and is directed horizontally tothe left as viewed in FIG. 8. From this point, unless interrupted by anobject in its path, beam 240 retraces its path and is verticallytransposed back down into the lightguide 215 by the vertical light pipe254. Unfilled arrowheads indicate the direction of the beam 240 after ithas been reflected off of reflector 260.

After being reflected back into the lightguide 215, the beam 240reflects off the vertical parabolic mirror 220 and is directed backthrough the lightguide 215 to the oscillating mirror 216, and thenceback through the light guide 215, the refracting surface 214 (see FIG.7), and to the half-silvered mirror 212 as described above.

Shown in FIG. 9 is a partially cut away keyboard 280 embodyingprinciples of the present invention. The keyboard 280 takes advantage ofthe vertical transposition of the light grid 252 by the opticaldigitizer 200 described above, to position the light grid 252 above keys282 disposed on the keyboard 280.

Keyboard 280 has a housing 284 which supports a keypad 286. The keys 282are distributed about the keypad 286 and include a space bar 288.Beneath the keypad 286, components of the optical digitizer 200 (morecompletely described hereinabove and representatively illustrated inFIGS. 7 and 8), including the light source 202, half-silvered mirror212, photodiode 262, lightguide 215, horizontal and vertical parabolicmirrors 222,220, and oscillating mirror 216, are contained within thekeyboard housing 284.

Horizontal and vertical light pipes 256 and 254 vertically transpose thelight grid 252 so that it is disposed above the keys 282. In thismanner, a user may utilize a finger or other object to interrupt thelight grid 252 above the keys 282 in order to indicate a position on acomputer screen as more fully described hereinabove. It is to beunderstood that the light grid 252 may be otherwise utilized withoutdeparting from the principles of the present invention.

Horizontal reflector 258 is attached to the space bar 288, facing thehorizontal light pipe 256, similar to the manner in which reflector 70is attached to space bar 88 in optical digitizer 10 representativelyillustrated in FIG. 3. Horizontal and vertical light pipes 256 and 254extend through the keypad 286 so that the light grid 252 is verticallytransposed above the keys 282. In this configuration, referring also toFIG. 8, the keypad 286 is disposed vertically between the right anglereflector 264 and reflector 266 of the vertical light pipe 254.

It is to be understood that the light pipes 254 and 256 may be otherwiseconstructed and mounted to the keypad 256 without departing from theprinciples of the present invention. For example, the light pipes may beconstructed so that they telescope into and out of the keypad 256. Inthis manner, the keyboard 280 may be made to more compactly nest againsta computer screen for compact storage.

Illustrated in FIG. 10 is another preferred embodiment of an opticaldigitizer 300 which embodies principles of the present invention. It isshown in highly schematicized form for the purpose of clarity. Dashedlines and arrows are used to represent paths and directions,respectively, of light. Filled arrowheads represent directions of lightin one plane and unfilled arrowheads represent directions of light thathas been transposed to another plane in a manner that will become clearupon consideration of the detailed description hereinbelow.

In the optical digitizer 300 illustrated in FIG. 10, similar to theoptical digitizer 200 illustrated in FIG. 7, light is reflected in morethan one plane. Elements of the optical digitizer 300 representativelyillustrated in FIG. 10, which have substantially the same function andstructure as elements representatively illustrated in FIG. 7, have beenidentified in FIG. 10 with the same item numbers, and are not furtherdescribed hereinbelow, unless such further description is helpful tofully and completely describe the optical digitizer 300.

A light source 202 provides a compact beam of light 204 which is in theinfrared portion of the light spectrum in the illustrated preferredembodiment. The beam 204 next passes through a refracting surface 214and into substantially transparent lightguide 215. Note that opticaldigitizer 300 as representatively illustrated does not include a beamsplitter or half-silvered mirror. The beam 204 next passes to anoscillating mirror 216. The beam 204 reflects off of the oscillatingmirror 216, producing a beacon 218.

The beacon 218 is directed by the oscillating mirror 216 to sweep acrosstwo parabolic mirrors, one of which 220 is oriented generally verticalas viewed in FIG. 10, and the other of which 222 is oriented generallyhorizontal as viewed in FIG. 10. A portion of the beacon 218, the"vertical" component 224 sweeps across the vertical parabolic mirror220. Likewise, a "horizontal" beacon component 226 sweeps across thehorizontal parabolic mirror 222.

When the horizontal component 226 reflects off of the horizontalparabolic mirror 222, it is directed in an upward direction as viewed inFIG. 10. The lowermost limit of the horizontal component 226,illustrated as a beam 228, once reflected off of the horizontalparabolic mirror 222, becomes the leftmost limit of a horizontal beaconportion 230 as viewed in FIG. 10. The uppermost limit of the horizontalcomponent 226, illustrated as a beam 232, once reflected off of thehorizontal parabolic mirror 222, becomes the rightmost limit of thehorizontal beacon portion 230 as viewed in FIG. 10.

Vertical component 224 of the beacon 218, after reflecting off of theoscillating mirror 216, strikes the vertical parabolic mirror 220 whichis constructed in a manner similar to the horizontal parabolic mirror222 in the illustrated preferred embodiment. A beam 238, lowermost inthe vertical component 224 as illustrated in FIG. 10, strikes thevertical parabolic mirror 220 and is reflected to the left in adirection orthogonal to the horizontal beacon portion 230. A beam 240,uppermost in the vertical component 224, strikes the vertical parabolicmirror 220 and is also directed to the left, orthogonal to horizontalbeacon portion 230 as illustrated in FIG. 10. Thus, it can be seen thatvertical component 224 of the beacon 218 is reflected off of verticalparabolic mirror 220 so that it sweeps vertically, as illustrated inFIG. 10, between the representatively shown beams 238 and 240, forming avertical beacon portion 242 which is orthogonal to horizontal beaconportion 230.

Beam 240 intersects beam 228 at point 244 and intersects beam 232 atpoint 246. Beam 238 intersects beam 228 at point 248 and intersects beam232 at point 250. Since the horizontal beacon portion 230 is orthogonalto the vertical beacon portion 242, points 244, 246, 248, and 250 definethe corners of a rectangular light grid 252. In this light grid 252, thehorizontal beacon portion 230 sweeps from side to side, and the verticalbeacon portion 242 sweeps from top to bottom, as representativelyillustrated in FIG. 10.

In a unique manner more fully described hereinbelow, the horizontal andvertical beacon portions 230 and 242, and the light grid 252 definedthereby are transferred to another plane, different from a plane inwhich the components of the optical digitizer 300 heretofore describedlie. Thus, the light source 202, lightguide 215, oscillating mirror 216,horizontal parabolic mirror 222, and vertical parabolic mirror 220 alllie in a plane as representatively illustrated in FIG. 10. The lightbeam 204 and some of its permutations (vertical portion 242, horizontalportion 230, and light grid 252), however, coexist on another,transposed, plane.

This transposition is accomplished by means of two light pipes, avertical light pipe 254 which vertically transposes the vertical beaconportion 242 and is generally vertically oriented as shown in FIG. 10,and a horizontal light pipe 256 which vertically transposes thehorizontal beacon portion 230 and is generally horizontally oriented asshown in FIG. 10. Vertical light pipe 254 takes the leftwardly directedvertical beacon portion 242, transposes it, and directs it to the rightas viewed in FIG. 10. Horizontal light pipe 256 takes the upwardlydirected horizontal beacon portion 230, transposes it, and directs itdownward as viewed in FIG. 10. Light pipes 254 and 256 are describedmore fully above in the detailed description accompanying FIG. 8.Directions of beams which have been transposed are indicated in FIG. 10with unfilled arrowheads.

After the horizontal beacon portion 230 has been transposed and directeddownward by the horizontal light pipe 256, as described above, aconventional linear detector 302, representatively illustrated in FIG.10 as being horizontally disposed at the lowermost extent of horizontalbeacon portion 230, senses light intensity along its length. The lineardetector 302 is of the type that is capable of indicating the lightintensity of a beam which strikes anywhere on its upwardly facing (asviewed in FIG. 10) surface 306. In a similar manner, conventional lineardetector 304, representatively illustrated in FIG. 10 as beingvertically disposed at the right-hand edge of vertical beacon portion242, senses the light intensity along its length of the beam 204 in thevertical beacon portion 242.

Plotting the light intensity over time as sensed by the horizontal andvertical linear detectors 302,304 will yield plots which aresubstantially the same as those representatively illustrated in FIGS.6A-6E, with the exception that the vertical and horizontal sweeps willbe separated, because they are sensed by separate linear detectors302,304, and there will be no increase in light intensity 108 betweenthe horizontal and vertical sweeps. Note that there is no need todiscriminate between horizontal and vertical sweeps since these aresensed by separate detectors 302,304.

Other methods of measuring the beam's horizontal and vertical positionmay be used without deviating from the principles of the presentinvention. Use of the preferred embodiment apparatus illustrated in FIG.10, and the resulting measurements of the intensity of the beam 204 overtime (see FIGS. 6A-6E), allow the position of an object in the lightgrid 252 to be determined as described hereinabove.

It will be readily apparent to one of ordinary skill in the art that thelight grid 252 of the optical digitizer 300 representatively illustratedin FIG. 10 may be disposed overlying a keyboard, and the light source202, lightguide 215, oscillating mirror 216, and horizontal and verticalparabolic mirrors 222 and 220 may be disposed beneath the keyboard aswith the optical digitizer 200 representatively illustrated in FIG. 9.If such an arrangement is desired, horizontal linear detector 302 can besubstituted for the reflector 258 on the space bar, and vertical lineardetector 304 can be substituted for the reflector 260 to the right ofthe keys as representatively illustrated in FIG. 9.

Shown in FIG. 11 is a keyboard 310 embodying principles of the presentinvention. The keyboard 310 takes advantage of the verticaltransposition of the light grid 252 by the optical digitizer 300described above, to position the light grid 252 above keys 282 disposedon the keyboard 310, in a manner similar to the keyboard 280representatively illustrated in FIG. 9. In the keyboard 310 illustratedin FIG. 11, however, the optical digitizer 300 is substituted for theoptical digitizer 200. Elements of keyboard 310 that are substantiallysimilar in function and structure are identified with the same itemnumbers in FIG. 11 as in FIG. 9.

Keyboard 310 has a housing 284 which supports a keypad 286. The keys 282are distributed about the keypad 286 and include a space bar 288.Beneath the keypad 286, components of the optical digitizer 300 (morecompletely described hereinabove and representatively illustrated inFIG. 10), including the light source 202, lightguide 215, horizontal andvertical parabolic mirrors 222,220, and oscillating mirror 216, arecontained within the keyboard housing 284.

Horizontal and vertical light pipes 256 and 254 vertically transpose thelight grid 252 so that it is disposed above the keys 282. In thismanner, a user may utilize a finger or other object to interrupt thelight grid 252 above the keys 282 in order to indicate a position on acomputer screen as more fully described hereinabove. It is to beunderstood that the light grid 252 may be otherwise utilized withoutdeparting from the principles of the present invention.

Horizontal linear detector 302 is attached to the space bar 288, facingthe horizontal light pipe 256, similar to the manner in which horizontalreflector 258 is attached to space bar 288 in optical digitizer 200representatively illustrated in FIG. 9. Horizontal and vertical lightpipes 256 and 254 extend through the keypad 286 so that the light grid252 is vertically transposed above the keys 282.

It is to be understood that the light grid 252 may be positionedrelative to other structures, such as a flat planar surface or a curvedsurface, without deviating from the principles of the present invention.It is also to be understood that light grid 252 may be in more than oneplane above the keypad 286, the vertical and horizontal beacon portions230 and 242 (see FIG. 10) being vertically transposed by the light pipes254 and 256 to different planes above the keypad 286, enabling thevelocity of an object obstructing the transposed beacon portions 230 and242 to be calculated as more fully described hereinabove.

The foregoing detailed description is to be clearly understood as beinggiven by way of illustration and example only, the spirit and scope ofthe present invention being limited solely by the appended claims.

What is claimed is:
 1. A method of optically sensing an object'sposition, said method comprising the steps of:generating a light beamhaving substantially parallel sides; converting said light beam to anoscillating beacon, said oscillating beacon having first and seconddifferently directed portions, said first and second beacon portionsbeing disposed in a first plane; intercepting and reflecting at leastone of said first and second oscillating beacon portions in said firstplane; transposing said at least one of said first and second beaconportions to a second plane, said second plane being offset from saidfirst plane; interposing the object in the path of said at least one ofsaid first and second beacon portions to interrupt it; sensing theinterruption of said at least one of said first and second beaconportions in said second plane; and utilizing the sensed interruption todetermine the position of the interposed object in said second plane. 2.The method of claim 1, wherein:said method further comprises the step ofpositioning said second plane upwardly adjacent a top side of a computerkeyboard; and the object is a finger of a user of said keyboard.
 3. Themethod of claim 2, further comprising the steps of positioning saidfirst plane within said computer keyboard, said computer keyboardincluding a keypad and a housing, and disposing said first planeintermediate said keypad and said housing.
 4. A method of sensing anobject's position, said method comprising the steps of:causing a lightsource to emit light rays; collimating a portion of said light rays sothat said light rays form a light beam having substantially parallelsides; directing said beam into a beacon producing means, therebyproducing a beacon in a first plane; reflecting said beacon off of areflecting means, so that said beacon is separated into at least firstand second beacon portions; transposing said first beacon portion to asecond plane different from said first plane utilizing a firsttransposing means; transposing said second beacon portion to a thirdplane different from said first plane utilizing a second transposingmeans; and sensing said first and second beacon portions with a lightsensing means, whereby, if the object obstructs said first or saidsecond beacon portions, said light sensing means will sense acorresponding absence of said light rays, and the position of the objectmay be calculated.
 5. The method according to claim 4, wherein in saidbeam directing step said beacon producing means comprises an oscillatingmirror.
 6. The method according to claim 4, further comprising the stepof directing said first beacon portion and said second beacon portion sothat said second and third planes are coplanar.
 7. The method accordingto claim 4, further comprising the step of directing said first beaconand said second beacon portion so that they are orthogonal to eachother.
 8. The method according to claim 4, further comprising the stepof:mounting said first and second transposing means and said reflectingmeans to a computer keyboard.
 9. The method according to claim 4,further comprising the step of:passing said beam through a beamsplitter.
 10. The method according to claim 9, further comprising thesteps of:reflecting said first beacon portion in said second plane sothat said first beacon portion is reflected back to said beam splitter;and reflecting said second beacon portion in said third plane so thatsaid second beacon portion is reflected back to said beam splitter. 11.The method according to claim 10, further comprising the step ofdirecting said first beacon portion and said second beacon portion sothat they are orthogonal to each other.
 12. The method according toclaim 11, further comprising the step of:disposing a keypad intermediatesaid first plane and said second plane.
 13. The method according toclaim 4, wherein in said beacon reflecting step said reflecting meanscomprises a parabolic mirror.
 14. Apparatus for sensing an object'sposition, comprising:first means for generating a light beam havingsubstantially parallel sides and converting said light beam to a beacon,said beacon sweeping across a first plane; second means for dividingsaid beacon into first and second differently directed portions; thirdmeans for converting said first and second differently directed beaconportions to transposed first and second beacon portions into which theobject may be interruptingly interposed, said transposed first andsecond beacon portions sweeping across second and third planes,respectively, each of said second and third planes being different fromsaid first plane; and fourth means for sensing an interruption of atleast one of said first and second transposed beacon portions andutilizing the sensed interruption to determine the position of theinterposed object.
 15. The apparatus of claim 14, furthercomprising:fifth means for associating said apparatus with a computerkeyboard in a manner such that said first and second transposed beaconportions are positioned upwardly adjacent a top side of said keyboard,such that said first and second transposed beacon portions are capableof being selectively intercepted and interrupted by a finger of a userof said keyboard.
 16. Apparatus for sensing an object's position, saidapparatus comprising:a light source, said light source emitting lightrays; a collimator, said collimator being operative to cause a portionof said light rays to form a light beam having substantially parallelsides; means disposed in said beam's path for producing a beacon fromsaid beam; means disposed in said beacon's path for separating saidbeacon into first and second beacon portions; first transposing meansdisposed in said first beacon portion's path for transposing said firstbeacon portion; second transposing means disposed in said second beaconportion's path for transposing said second beacon portion; and lightsensing means for sensing said first and second transposed beaconportions, whereby, the position of the object may be convenientlycalculated when the object obstructs said first and second transposedbeacon portions.
 17. The apparatus according to claim 16, wherein saidbeacon producing means comprises an oscillating mirror.
 18. Theapparatus according to claim 16, wherein said first beacon portion andsaid second beacon portion are coplanar.
 19. The apparatus according toclaim 18, wherein said first and second transposed beacon portions arecoplanar.
 20. The apparatus according to claim 19, wherein said firstand second transposed beacon portions are orthogonal to each other. 21.The apparatus according to claim 16, further comprising:a computerkeyboard; and said first and second transposing means are mounted tosaid computer keyboard.
 22. The apparatus according to claim 16,wherein:said first transposed beacon portion sweeps a first plane; andsaid second transposed beacon portion sweeps a second plane, said secondplane being in an overlapping, parallel, and spaced apart relationshipto said first plane, whereby, the object's velocity may be convenientlycalculated by timing the difference between an obstruction of said firsttransposed beacon portion and a corresponding obstruction of said secondtransposed beacon portion.
 23. The apparatus according to claim 22,wherein said first and second transposed beacon portions are orthogonalto each other.
 24. The apparatus according to claim 22, furthercomprising:a computer keyboard; and said first plane and said secondplane being in an overlapping and spaced apart relationship to saidcomputer keyboard.
 25. A computer keyboard device of the type having agenerally planar keypad with a plurality of keys disposed on the keypad,and a housing supporting the keypad, and further having the capabilityof detecting the position of an object, said computer keyboard devicecomprising:a reflector, said reflector being mounted intermediate thekeypad and the housing; a beacon producer, said beacon producer beingmounted intermediate the keypad and the housing, and being positioned sothat a beacon of light is directed to sweep repeatedly across saidreflector to produce a reflected light beacon in a first plane; a beacontransposer for transposing said reflected light beacon to a secondplane; and a light sensor for measuring the intensity of light receivedtherein, said light sensor being positioned to receive said transposedand reflected light beacon therein.
 26. The device according to claim25, wherein:said beacon producer is mounted so that said beacon of lightis directed to sweep across said first plane in a substantiallytransparent lightguide, said lightguide having said reflector formed onan edge surface thereof.
 27. The device according to claim 25, whereinsaid reflector further comprises first and second parabolic mirrors forreflecting said beacon of light and dividing said beacon of light intofirst and second beacon portions.
 28. The device according to claim 27wherein said first and second parabolic mirrors are configured so thatsaid first and second beacon portions are orthogonal to each other. 29.The device according to claim 27 wherein said transposer comprises firstand second light pipes, said first and second light pipes beingpositioned so that said first and second beacon portions are orthogonalto each other in said second plane.
 30. An optical digitizer,comprising:a light source, said light source producing a beam of light;a beacon generator, said beacon generator producing a beacon from saidbeam of light, said beacon including a first beacon portion; a firstreflector, said first reflector reflecting said first beacon portion;and a first light pipe, said first light pipe transposing said reflectedfirst beacon portion such that said transposed first beacon portion doesnot intersect said reflected first beacon portion.
 31. The opticaldigitizer according to claim 30, wherein said beacon includes a secondbeacon portion, and further comprising a second reflector, said secondreflector reflecting said second beacon portion, and a second lightpipe, said second light pipe transposing said reflected second beaconportion such that said transposed second beacon portion does notintersect said reflected second beacon portion.
 32. The opticaldigitizer according to claim 31, further comprising third and fourthreflectors, a beam splitter, and a light sensor, said third reflectorreflecting said transposed first beacon portion back to said first lightpipe, said fourth reflector reflecting said transposed second beaconportion back to said second light pipe, said beam splitter reflectingsaid first and second beacon portions toward said light sensor aftersaid first and second beacon portions have been reflected off of saidthird and fourth reflectors, respectively, and said light sensor sensingintensity of said first and second beacon portions.
 33. The opticaldigitizer according to claim 30, further comprising a substantiallytransparent lightguide, said lightguide having said first reflectorformed on a first surface of said lightguide.
 34. The optical digitizeraccording to claim 33, wherein said lightguide further has a secondsurface disposed between said light source and said beacon generator,said lightguide second surface refracting said beam between said lightsource and said beacon generator.
 35. The optical digitizer according toclaim 30, wherein said beacon generator is an oscillating mirror. 36.The optical digitizer according to claim 30, wherein said firstreflector is curved.
 37. The optical digitizer according to claim 36,wherein said curved first reflector causes said first beacon portion todefine a light grid having a predetermined shape when said first beaconportion reflects off of said curved first reflector.
 38. The opticaldigitizer according to claim 30, further comprising a first linearsensor, said first linear sensor sensing intensity of said transposedfirst beacon portion.
 39. The optical digitizer according to claim 38,wherein said beacon includes a second beacon portion, and furthercomprising a second reflector, said second reflector reflecting saidsecond beacon portion, a second light pipe, said second light pipetransposing said reflected second beacon portion such that saidtransposed second beacon portion does not intersect said reflectedsecond beacon portion, and a second linear sensor, said second linearsensor sensing intensity of said transposed second beacon portion.
 40. Amethod of optically sensing an object's position, said method comprisingthe steps of:generating a light beam; converting said light beam to abeacon, said beacon having first and second differently directedportions, said first and second beacon portions being disposed in afirst plane; transposing at least one of said first and second beaconportions to a second plane, said second plane being offset from saidfirst plane; interposing the object in the path of said at least one ofsaid first and second beacon portions to interrupt it; sensing theinterruption of said at least one of said first and second beaconportions in said second plane; and utilizing the sensed interruption todetermine the position of the interposed object in said second plane.